In the related art, an optical scanning device that can substantially increase the scanning rate of laser light is known (for example, see Patent Literature 1). The optical scanning device discussed in Patent Literature 1 includes a beam splitter that reflects and transmits a laser beam so as to split the laser beam; a half mirror that reflects the laser beam transmitted through the beam splitter; a scanner that scans the laser beams reflected at different output angles from the beam splitter and the half mirror; and a diaphragm that selectively allows the laser beams scanned by the scanner to pass therethrough.
The optical scanning device discussed in Patent Literature 1 makes the scanner simultaneously scan the laser beams reflected by the beam splitter and the half mirror and allows only one of the laser beams to pass sequentially through the diaphragm so that multiple light beams are sequentially scanned in a single scanning process of the scanner, thereby shortening the time required for scanning a specific area.